<p>Consider a complex unital Banach algebra <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathcal {A}.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">A</mi> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> For <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(x_1,x_2,x_3\in \mathcal {A},\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> <mo>,</mo> <msub> <mi>x</mi> <mn>3</mn> </msub> <mo>∈</mo> <mi mathvariant="script">A</mi> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> in this paper, we establish that under certain assumptions on <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(x_1,x_2,x_3\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> <mo>,</mo> <msub> <mi>x</mi> <mn>3</mn> </msub> </mrow> </math></EquationSource> </InlineEquation>, Drazin (resp. g-Drazin) invertibility of any three elements among <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(x_1,x_2,x_3\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> <mo>,</mo> <msub> <mi>x</mi> <mn>3</mn> </msub> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(x_1+x_2+x_3~(\text {or }x_1x_2+x_1x_3+x_2x_3)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> <mo>+</mo> <msub> <mi>x</mi> <mn>3</mn> </msub> <mspace width="3.33333pt" /> <mrow> <mo stretchy="false">(</mo> <mtext>or</mtext> <mspace width="0.333333em" /> <msub> <mi>x</mi> <mn>1</mn> </msub> <msub> <mi>x</mi> <mn>2</mn> </msub> <mo>+</mo> <msub> <mi>x</mi> <mn>1</mn> </msub> <msub> <mi>x</mi> <mn>3</mn> </msub> <mo>+</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> <msub> <mi>x</mi> <mn>3</mn> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> ensure the Drazin (resp. g-Drazin) invertibility of the remaining one. As a consequence for two idempotents <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(p,q\in \mathcal {A},\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>p</mi> <mo>,</mo> <mi>q</mi> <mo>∈</mo> <mi mathvariant="script">A</mi> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> this result indicates the equivalence between Drazin (resp. g-Drazin) invertibility of <Equation ID="Equ22"> <EquationSource Format="TEX">\(\lambda _1p+\gamma _1q-\lambda _1pq+\lambda _2\left( pqp-(pq)^2\right) +\cdots +\lambda _m\left( (pq)^{m-1}p-(pq)^m\right) \)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <msub> <mi>λ</mi> <mn>1</mn> </msub> <mi>p</mi> <mo>+</mo> <msub> <mi>γ</mi> <mn>1</mn> </msub> <mi>q</mi> <mo>-</mo> <msub> <mi>λ</mi> <mn>1</mn> </msub> <mi>p</mi> <mi>q</mi> <mo>+</mo> <msub> <mi>λ</mi> <mn>2</mn> </msub> <mfenced close=")" open="("> <mi>p</mi> <mi>q</mi> <mi>p</mi> <mo>-</mo> <msup> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mn>2</mn> </msup> </mfenced> <mo>+</mo> <mo>⋯</mo> <mo>+</mo> <msub> <mi>λ</mi> <mi>m</mi> </msub> <mfenced close=")" open="("> <msup> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mi>p</mi> <mo>-</mo> <msup> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mi>m</mi> </msup> </mfenced> </mrow> </math></EquationSource> </Equation>and <Equation ID="Equ23"> <EquationSource Format="TEX">\(\lambda _1-\lambda _1pq+\lambda _2\left( pqp-(pq)^2\right) +\cdots +\lambda _m\left( (pq)^{m-1}p-(pq)^m\right) ,\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <msub> <mi>λ</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>λ</mi> <mn>1</mn> </msub> <mi>p</mi> <mi>q</mi> <mo>+</mo> <msub> <mi>λ</mi> <mn>2</mn> </msub> <mfenced close=")" open="("> <mi>p</mi> <mi>q</mi> <mi>p</mi> <mo>-</mo> <msup> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mn>2</mn> </msup> </mfenced> <mo>+</mo> <mo>⋯</mo> <mo>+</mo> <msub> <mi>λ</mi> <mi>m</mi> </msub> <mfenced close=")" open="("> <msup> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mi>p</mi> <mo>-</mo> <msup> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mi>m</mi> </msup> </mfenced> <mo>,</mo> </mrow> </math></EquationSource> </Equation>where <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\gamma _1,\lambda _i\in \mathbb {C}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>γ</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>λ</mi> <mi>i</mi> </msub> <mo>∈</mo> <mi mathvariant="double-struck">C</mi> </mrow> </math></EquationSource> </InlineEquation> for <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(i=1,2,\cdots ,m,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mo>⋯</mo> <mo>,</mo> <mi>m</mi> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> with <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\lambda _1\gamma _1\ne 0;\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>λ</mi> <mn>1</mn> </msub> <msub> <mi>γ</mi> <mn>1</mn> </msub> <mo>≠</mo> <mn>0</mn> <mo>;</mo> </mrow> </math></EquationSource> </InlineEquation> which extend the work of Barraa and Benabdi [<CitationRef CitationID="CR1">1</CitationRef>]. Furthermore, for <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(x_1,x_2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> </mrow> </math></EquationSource> </InlineEquation>, we establish that the Drazin (resp. g-Drazin) invertibility of any two elements among <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(x_1,x_2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(x_1+x_2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> </mrow> </math></EquationSource> </InlineEquation> indicates the Drazin (resp. g-Drazin) invertibility of the remaining one, provided that <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(x_1x_2=\alpha (x_1+x_2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <msub> <mi>x</mi> <mn>2</mn> </msub> <mo>=</mo> <mi>α</mi> <mrow> <mo stretchy="false">(</mo> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for some <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(\alpha \in \mathbb {C}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo>∈</mo> <mi mathvariant="double-struck">C</mi> </mrow> </math></EquationSource> </InlineEquation>. Additionally, if it exists, we furnish a new formula to represent the Drazin (resp. g-Drazin) inverse of any element among <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(x_1,x_2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq16"> <EquationSource Format="TEX">\(x_1+x_2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>x</mi> <mn>2</mn> </msub> </mrow> </math></EquationSource> </InlineEquation>, by using the other two elements and their Drazin (resp. g-Drazin) inverse.</p>

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Equivalency of Drazin and g-Drazin invertibility of elements in a Banach algebra

  • Rounak Biswas,
  • Falguni Roy

摘要

Consider a complex unital Banach algebra \(\mathcal {A}.\) A . For \(x_1,x_2,x_3\in \mathcal {A},\) x 1 , x 2 , x 3 A , in this paper, we establish that under certain assumptions on \(x_1,x_2,x_3\) x 1 , x 2 , x 3 , Drazin (resp. g-Drazin) invertibility of any three elements among \(x_1,x_2,x_3\) x 1 , x 2 , x 3 and \(x_1+x_2+x_3~(\text {or }x_1x_2+x_1x_3+x_2x_3)\) x 1 + x 2 + x 3 ( or x 1 x 2 + x 1 x 3 + x 2 x 3 ) ensure the Drazin (resp. g-Drazin) invertibility of the remaining one. As a consequence for two idempotents \(p,q\in \mathcal {A},\) p , q A , this result indicates the equivalence between Drazin (resp. g-Drazin) invertibility of \(\lambda _1p+\gamma _1q-\lambda _1pq+\lambda _2\left( pqp-(pq)^2\right) +\cdots +\lambda _m\left( (pq)^{m-1}p-(pq)^m\right) \) λ 1 p + γ 1 q - λ 1 p q + λ 2 p q p - ( p q ) 2 + + λ m ( p q ) m - 1 p - ( p q ) m and \(\lambda _1-\lambda _1pq+\lambda _2\left( pqp-(pq)^2\right) +\cdots +\lambda _m\left( (pq)^{m-1}p-(pq)^m\right) ,\) λ 1 - λ 1 p q + λ 2 p q p - ( p q ) 2 + + λ m ( p q ) m - 1 p - ( p q ) m , where \(\gamma _1,\lambda _i\in \mathbb {C}\) γ 1 , λ i C for \(i=1,2,\cdots ,m,\) i = 1 , 2 , , m , with \(\lambda _1\gamma _1\ne 0;\) λ 1 γ 1 0 ; which extend the work of Barraa and Benabdi [1]. Furthermore, for \(x_1,x_2\) x 1 , x 2 , we establish that the Drazin (resp. g-Drazin) invertibility of any two elements among \(x_1,x_2\) x 1 , x 2 and \(x_1+x_2\) x 1 + x 2 indicates the Drazin (resp. g-Drazin) invertibility of the remaining one, provided that \(x_1x_2=\alpha (x_1+x_2)\) x 1 x 2 = α ( x 1 + x 2 ) for some \(\alpha \in \mathbb {C}\) α C . Additionally, if it exists, we furnish a new formula to represent the Drazin (resp. g-Drazin) inverse of any element among \(x_1,x_2\) x 1 , x 2 and \(x_1+x_2\) x 1 + x 2 , by using the other two elements and their Drazin (resp. g-Drazin) inverse.